Browsing by Author "Michler, Peter (Prof. Dr.)"

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Open Access
InP/(Al,Ga)InP quantum dots on GaAs- and Si-substrates for single-photon generation at elevated temperatures
(2013) Bommer, Moritz; Michler, Peter (Prof. Dr.)
This work concentrates on optical investigation on single-photon generation for applications in communications, quantum cryptography, and quantum computing. Single-photon sources for commercial devices require robustness in their working conditions, e.g. temperature, pressure, etc. as well as high output rates and emission directionality. From the many possibilities of generating single-photons like single-atoms, parametric down-conversion, nitrogen vacancy centers in diamond etc., InP quantum dots have been chosen for detailed analysis in this thesis. The InP and InAs quantum dots discussed in this work, are epitaxially fabricated by MOVPE in the Stranski-Krastanov growth-mode. In order to access a single quantum dot, different approaches of processing and pre-processing like shadow masks, mesas, micro-pillars, and site-controlled growth are employed. The quantum dots have been fabricated on different substrates, namely miscut and exactly oriented GaAs, Si, and Ge virtual substrate on Si. The latter two might allow complementary metal oxide semiconductor (CMOS)-compatibility, which is of high interest because it allows the integration of optical elements into the commercially well established Si based environment. Here, the influence of different substrates on the single-photon emission properties of quantum dots has been investigated. For detailed analysis of the fabricated samples, various measurement techniques like X-ray diffraction, secondary ion mass spectrometry, scanning electron microscopy, atomic-force microscopy, photoluminescence spectroscopy on single quantum dots and ensembles of quantum dots, TCSPC, and photon statistics measurements were utilized. The main focus of this work lies on the latter, optical measurements of single quantum dots. Extending the temperature range for InP quantum dots based single-photon sources from the current maximum temperature of 80K towards the regime of Peltier-cooling (≥ 150K) is very desirable, because it reduces the footprint of a device and its servicing costs drastically. In this work, an enhancement of the working temperature up to 110K, with g⁽²⁾_deconv.(τ = 0) = 0.41, has been shown. Therefore, detailed temperature dependent studies on the physics of single-photon generation have been performed. The thermal activation of charge carriers into the barrier, limiting their working temperature and especially, the spectral linewidth broadening by temperature, with respect to the biexciton binding energy, has been investigated in detail. The results of these studies have been used to build a model of the exciton-biexciton-system. The model extrapolates the temperatures of the system up to 200K. Out of this model, the influence of a spectral biexciton-exciton-overlap and the exciton dark-state on single-photon generation has been investigated.
Unknown
Mollow triplet emission properties and dephasing effects in semiconductor quantum dots
(2013) Weiler, Stefanie; Michler, Peter (Prof. Dr.)
The thesis presents the investigations of the emission properties of the Mollow triplet (resonance fluorescence above emitter saturation) and dephasing effects in semiconductor quantum dots. The investigations of the Mollow triplet emission properties focus on the detuning dependent Mollow triplet emission especially the relative areas and width of the individual Mollow peaks. If both fine-structure components of the exciton are excited a Mollow quintuplet is experimentally observed, which is found to be in agreement with a theoretical model. In addition the indistinguishable photon emission from the individual Mollow sidebands is verified. The investigations on dephasing effects focus on the phonon-assisted incoherent excitation of a quantum dot and a comprehensive study of the emission properties under these excitation conditions. A second study focuses on the non-resonant emitter mode coupling of a quantum dot coupeld to two modes of the micro pillar cavity together with the corresponding emission properties.
Open Access
Optical and quantum optical properties of a quantum dot-atomic vapor interface
(2021) Vural, Hüseyin; Michler, Peter (Prof. Dr.)
The pathway to advanced quantum technological applications often includes hybrid quantum systems of matter mediated by quantum-states of light. This thesis examines a particular hybrid system formed by a single semiconductor quantum dot (QD) and cesium (Cs) atoms in a hot vapor. Pulsed resonant excitation of single InGaAs QDs is utilized to realize precisely timed emission of pure single and indistinguishable photons. This enables detailed studies of the interaction of one- and two-photon Fock-states with a hot Cs vapor within the framework of the slow-light effect. A delay line for both Fock-states is realized achieving high fractional delays, while the photon statistics of the transmitted light is investigated after the vapor. On that basis, via Hong-Ou-Mandel measurements, the implications of pulse distortion for future quantum networks that rely on two-photon interference is investigated. Moreover, the essential connection between dispersion and unique pulse distortion is exploited for a novel time-domain high-resolution spectroscopy. It allows to tackle the open problem of characterizing spectral diffusion dynamics of on-demand operated quantum emitters. With this method, assessing their performances for quantum optical applications by straightforward photon-correlation is achieved.
Open Access
Thin-film InGaAs metamorphic buffer for telecom C-band quantum dots and optical resonators
(2023) Sittig, Robert; Michler, Peter (Prof. Dr.)
The advent of quantum cryptography applications holds the prospect of opening a new chapter of telecommunication. One vital building block for these technologies is access to efficient non-classical light sources. Recent breakthroughs have been reported in the effort of attaining high-quality single-photon emission from quantum dots inside the crucial telecom C-band. One attractive route in this regard is to apply additional strain-engineering to the established InAs-on-GaAs material system by inserting a metamorphic buffer. This approach has already demonstrated promising optical properties. However, an integration of these quantum dot emitters into an advanced photonic structure to enhance extraction efficiency and to utilize beneficial cavity effects is still missing. This thesis aims at establishing an InGaAs metamorphic buffer that facilitates compatibility with conventional photonic cavity structures as well as common lithography fabrication methods. For this purpose, a next-generation buffer design is proposed and discussed. Its non-linear, strain-optimized content grading enables maximum lattice transition at minimal thickness. This thin-film design is then realized via metal-organic vapour-phase epitaxy. Here, a comprehensive optimization of growth parameters is conducted to attain maximum crystalline quality. This process includes fine-tuning the quantum dot emission to 1550nm wavelength and an optimization for maximum brightness plus minimal fine-structure splitting. Furthermore, the completed layer stack is characterized structurally and design resiliencies within the buffer layer are explored. Markedly, a minimum feasible stable thickness of 170nm is found. Moreover, benchmark emission properties like single-photon purity, linewidth and decay time consistently exhibit favorable comparability to their traditional quantum dot system counterparts. Finally, the integration of the thinfilm metamorphic structure into various exemplary advanced photonic cavities is investigated. Critically, the feasibility of necessary design adaptations is examined, determining flexibilities and limitations. The presented results constitute a significant step towards the fabrication of high-quality single-photon sources inside the telecom C-band based on semiconductor quantum dots. Accordingly, the obtained progress will boost the real world implementation of emerging communication technologies based on non-classical light.